As agents for the circulatory system, particularly therapeutic agents for hypertension, various compounds are commercially available or currently under development. In recent years, the possibility of treatment of circulatory diseases based on a new mechanism called "potassium channel opener" has been suggested and various investigations have been made, based on this theory.
Typical examples of drugs based on the above mechanism are Pinacidil [N"-cyano-N-4-pyridyl-N'-(1,2,2-trimethylpropyl)guanidine] having an N-pyridyl-N'-cyanoguanidine skeleton and Cromakalim [(+,-)-6-cyano-3,4-dihydro -2,2-dimethyl-trans-4-(2-oxo-1-pyrrolidinyl)-2H -benzo(b)pyran-3-ol] having a benzopyran skeleton.
At present, however, it cannot be said that Pinacidil nor Cromakalim possess sufficient pharmacological effects without side effects. In particular, Pinacidil causes stagnation as a side effect, and the problems of edema, vascular headache, cardiopalmus, etc. remain unsolved.
In order to solve the above problems, new compounds thought to have an improved overall pharmacological effect are currently under investigation.
As such compounds, N-alkyl-N'-pyridyl-thioureas and N-alkyl-N'-pyridyl-N'-cyanoguanidines [JP-A-51-86474 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-52-83573 corresponding to U.S. Pat. No. 4,057,636] and N-substituted-N-aryl-thioureas and N-substituted-N-aryl-N'-cyanoguanidines (JP-A-2-91057 corresponding to EP 354553 and JP-A-2-290841 corresponding to EP 392802) have been reported.